Placer County Water Agency plans spillway modifications to handle the probable maximum flood at L.L. Anderson Dam, part of the 223.753-MW Middle Fork American River project in California.
The water agency said it will modify the spillway to safely pass an inflow of 59,100 cubic feet per second for the probable maximum flood. The existing inflow is 15,000 cfs.
The Federal Energy Regulatory Commission accepted the water agency’s plan and schedule for the spillway work, including a Potential Failure Mode Analysis session in October to review remedial repair options.
Engineering is to be completed in December 2008. Construction is to begin in April 2010, with the job to be completed in December 2010.
Work calls for adding 30 feet to the width of the 40-foot-wide spillway for the 231-foot-tall, 2,700-foot-long dam. Spillway gates also could be replaced or new gates added.
MWH is serving as engineer on the $20 million program.